The invention concerns a process and a control system for the control of the driveline of a utility vehicle that contains a power plant with fuel injection quantity control and an infinitely variable transmission (IVT), in which an initial engine rotational speed, an initial wheel rotational speed, the actual engine rotational speed and the actual wheel rotational speed are determined and stored in memory.
The driveline of utility vehicles, such as agricultural or commercial vehicles, generally contain an internal combustion engine and a transmission. The engine has the requirement that it supply the needed power with the best possible efficiency, while the transmission operates as torque and rotational speed converter adjusting the performance map of the engine to the demand map of the vehicle. In the further development of the driveline, beyond the aforementioned goals of increased productivity, operator comfort, other aspects come increasingly into the foreground, such as exhaust emissions and fuel consumption.
In order to attain these goals infinitely variable transmissions may be employed to great advantage, such as have been described in DE-A-35 33 193 and DE-A-41 15 623. These are hydrostatic-mechanical torque dividing transmissions with an infinitely variable hydrostatic component, consisting of adjustment pump and hydraulic motor, and a mechanical branch with several drive ratios that can be shifted automatically without interrupting the power flow. The drive ratio of these transmissions is infinitely variable over the entire operating range.
EP-A-0 280 757 describes a control and regulating arrangement for such an infinitely variable transmission. The actual engine rotational speed and the actual transmission output rotational speed are continuously determined and compared to the target signal. By continuously varying the drive ratio of the transmission and the engine rotational speed the control system reacts to changes in the target signals or the operating conditions. With increasing tractive resistance the engine rotational speed is initially reduced which results in an increase in the engine control signal in the drive control, in order to make available an increase in engine power. Furthermore the transmission drive ratio is adjusted in order to maintain or to attain the desired vehicle speed. The control system is to be designed in such a way that the transmission drive ratio as well as the engine rotational speed are continuously adjusted for optimum fuel economy.
Furthermore in a technical meeting in Dresden, Germany, in 1989 F. Jarchow proposed an infinitely variable hydrostatic-mechanical transmission for tractors that can be shifted under load and has a control that permits operation along a curve of minimum fuel consumption. On the basis of an optimum fuel consumption curve a voltage can be determined for each position of the gas pedal, which is compared with a voltage corresponding to the transmission input rotational speed. The voltage difference is used to adjust the transmission drive ratio.